1. Field of the Invention
The present invention relates to a method and apparatus for processing a control message. More particularly, the present invention relates to a method and apparatus for processing a control message that requests retransmission of data to prevent packet losses and unnecessary retransmissions.
2. Description of the Related Art
A Universal Mobile Telecommunication Service (UMTS) system is a third generation asynchronous mobile communication system based on Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS), which are European mobile communication systems, and uses Wideband Code Division Multiple Access (W-CDMA).
A Long Term Evolution (LTE) is being evolved as a next generation mobile communication system in a 3rd Generation Partnership Project (3GPP) which is currently in charge of UMTS standardization. The LTE is a technology that implements communication based on high-speed packets having a maximum of about 100 Mbps, and has a goal to be commercialized in the year 2010. For this, various methods are being evolved. For example, the various methods include a method for reducing a number of nodes positioned on a channel by simplifying a network structure and a method for providing wireless protocols close to a wireless channel.
FIG. 1 illustrates a conventional configuration of a next generation mobile communication system. Here, the configuration of the mobile communication system is based on a UMTS system.
Referring to FIG. 1, the mobile communication system includes Evolved Radio Access Networks (E-RANs) 110, 112 that are simplified as a two-node structure of evolved Node Bs (eNBs) or base stations 120, 122, 124, 126 and 128, and Evolved Packet Cores (EPCs) 130, 132, which is also none as upper nodes, such as Access Gateways. A User Equipment (UE) or user terminal 101 connects to an Internet Protocol (IP) network 114 by the E-RANs 110, 112.
The eNBs 120 to 128 correspond to an existing node B of the UMTS system and is connected to the UE 101 with a wireless channel. However, unlike the existing node B, eNB 120 to 128 plays complicated roles. In a Long Term Evolution (LTE), entire user traffic including real-time services, such as Voice over IP (VoIP) through the IP, is serviced through a shared channel, so that an apparatus which collects information of the UE 101 and performs scheduling is required. The scheduling is performed by the eNBs 120 to 128. In order to implement the maximum 100 Mbps, the LTE uses Orthogonal Frequency Division Multiplexing (OFDM) as a wireless connection technology with a maximum of 20 MHz bandwidth. Also, an Adaptive Modulation & Coding (AMC) method, which determines a modulation scheme and a channel coding rate according to the channel state of the terminal, is applied.
FIG. 2 is a drawing illustrating a conventional wireless protocol layer of a LTE system.
Referring to FIG. 2, the wireless protocol of the LTE system includes Packet Data Convergence Protocols (PDCPs) 205 and 240, Radio Link Controls (RLCs) 210 and 235, and Medium Access Controls (MACs) 215 and 230. The PDCPs 205 and 240 performs IP header compression/restoration, ciphering/deciphering, lossless handover support, and the like. After a handover between eNBs is completed, a lossless handover is accomplished as a PDCP status report having reception information that includes whether a PDCP Service Data Unit (SDU), which was not received by a PDCP layer, has been received is transmitted and another PDCP layer retransmits the data unit (i.e., the PDCP SDU) that was not received.
The PDCP status report may express reception information indicating the reception of a corresponding data unit through a Sequence Number (SN) of the data unit. The RLCs 210 and 235 perform an Automatic Retransmitting Request (ARQ) operation by reconfiguring a PDCP Packet Data Unit (PDU) (hereinafter, a packet output from a certain protocol layer apparatus is called a PDU of the protocol) with an appropriate size. The MACs 215 and 230 are connected to several RLC devices configured in one terminal. The MACs 215 and 230 also multiplex RLC PDUs into an MAC PDU and demultiplexes RLC PDUs from the MAC PDU.
Physical layers (PHYs) 220 and 225 perform channel coding and modulation for upper layer data, provide the data as OFDM symbols and transmit the OFDM symbols to a wireless channel. Alternatively, the PHYs 220 and 225 perform demodulation and channel decoding for OFDM symbols received through the wireless channel and transmits the OFDM symbols to the upper layer. Here, the PDCP status report does not express reception information indicating whether a corresponding data unit has been received.
Therefore, a need exists for a method and apparatus for efficiently receiving and transmitting reception information that indicates whether a data unit has been received.